1. Technical Field
The present disclosure relates to a liquid crystal display, and methods of fabricating and repairing the same, and more particularly, to a method of repairing a liquid crystal display with two sub-pixels in one pixel.
2. Discussion of the Related Art
Since a liquid crystal display (LCD) has advantages of small size, light weight and low power consumption as compared to a conventional cathode ray tube (CRT), the LCDs are widely favored over the CRTs.
An LCD is a device in which two substrates with electrodes formed thereon are positioned such that the two electrodes face each other, a liquid crystal substance is injected between the two substrates, and an electric field is then applied between the two electrodes to move liquid crystal molecules so that transmittance of light can vary, thereby displaying an image. A conventional LCD has a narrow viewing angle due to gray inversion generated from all liquid crystals of the LCD being oriented in one direction. Accordingly, studies on a technique for increasing the viewing angle of the LCD have been actively conducted in recent years.
A patterned vertical alignment (PVA) type LCD has been developed to improve the viewing angle of an LCD. Liquid crystals within the PVA type LCD are vertically aligned with respect to upper and lower substrates, and an aperture pattern, a protrusion pattern or the like is formed as a domain regulating means on a pixel electrode and a common electrode that is a counter electrode. However, a side visibility distortion phenomenon occurs in the conventional PVA type LCD.
An LCD provided with an S-PVA structure has been developed in response to the phenomenon. A unit pixel is constructed to have two sub-pixels and differential voltages are applied to the respective sub-pixels so that side gray level rounding or reversion can be relieved, thereby enhancing side visibility. Such an LCD comprises two transistors and two pixel electrode patterns within a region of one pixel for expressing one color, and naturally expresses gray levels using a method of differentiating peak voltages applied to the respective pixel electrode patterns so that the side visibility distortion phenomenon can be relieved.
However, where one of two sub-pixels constituting one pixel has a failure in a conventional S-PVA structure, the other sub-pixel should also be repaired. This complicates the repairing process and thus lowers the rate of a successful pixel repair.
S-PVA structures include a structure in which two thin film transistors (TFTs) driven through different gate lines share one data line and a structure in which two TFTs connected to different data lines share one gate line.
FIG. 1 illustrates a method of repairing a conventional LCD.
Referring to FIG. 1, the conventional LCD comprises first and second TFTs 21 and 22 connected to gate lines 10, first and second data lines 31 and 32 respectively connected to the first and second TFTs 21 and 22, first pixel patterns 41 connected to the first TFTs 21, second pixel patterns 42 connected to the second TFTs 22 and storage electrodes 50 overlapping with the first and second pixel patterns 41 and 42.
A protection film is formed on the first and second TFTs 21 and 22, and the first and second pixel patterns 41 and 42 are formed on the protection film.
The first TFT 21 is connected to the first pixel pattern 41 through a first drain contact plug 43, and the second TFT 22 is connected to the second pixel pattern 42 through a second drain contact plug 44. Further, the storage electrode 50 extends below the first and second drain contact plugs 43 and 44.
Accordingly, there is provided an LCD including a first sub-pixel with a first pixel pattern and a second sub-pixel with a second pixel pattern within a region of one pixel. Here, a gray level voltage with a lower peak value is applied to the first sub-pixel to express a lower gray level, and a gray level voltage with a higher peak value is applied to the second sub-pixel to express a higher gray level.
However, since two pixel patterns are provided within the region of one pixel and two TFTs for respectively driving them are included in the structure, a channel failure generating rate of the TFTs due to contaminations is twice that of a case where one TFT is provided for one pixel pattern. Further, the number of lines for use in driving a plurality of pixel patterns increases, and accordingly, a failure rate increases due to an increase in pattern density.
Furthermore, since the two sub-pixels constitute one pixel, when a failure occurs in one of the two sub-pixels, both the sub-pixels need to be repaired.
A pixel failure can be repaired by disconnecting the TFTs of the pixel from the corresponding pixel patterns. The first TFT 21 can be disconnected from the first pixel pattern 41 by using a laser to cut a region (see region B in FIG. 1) on an extension of the drain electrode 28 between the first TFT 21 and the first drain contact plug 43.
The first pixel pattern 41 and the lower storage electrode 50 are electrically connected by radiating a laser such that the first pixel pattern 41 is not floated and is off upon application of a storage voltage. If the first pixel pattern 41 is floated, a liquid crystal is driven by a voltage applied to a common electrode pattern (not shown). Thus, a storage voltage at the same level as the voltage applied to the common electrode pattern is applied to the first pixel pattern so that a sub-pixel including the first pixel pattern 41 becomes an off-pixel. To prevent the first pixel pattern 41 from being floated due to a connection failure, the laser is radiated twice at both edges of the first drain contact plug 43 (see regions C and D in FIG. 1). Accordingly, the sub-pixel including the first pixel pattern 41 is off.
Since the entire unit pixel becomes a low pixel if one sub-pixel is off, the entire unit pixel should become an off-pixel. Thus, an extension of the drain electrode 28 between the second TFT 22 and the second drain contact plug 44 should be cut using the laser so that the second TFT 22 can be disconnected from the second pixel pattern 42 (see region G in FIG. 1). The second pixel pattern 42 and the storage electrode 50 are electrically connected by radiating a laser twice at both edges of the contact plug 44 (see regions E and F in FIG. 1). Accordingly, the other sub-pixel including the second pixel pattern 42 is also off.
As described above, it requires six laser operations to repair the conventional LCD. Therefore, a need exists for a more efficient method of repairing an LCD.